The invention relates to a method of testing tires, wherein before and after an alteration in the tire pressure a respective interferogram is produced of the tire surface using coherent radiation and, from the interferogram, the information concerning any defects present in the tire is obtained, and furthermore to an apparatus for the performance of the method.
The German patent publication 42 31 578 A1 discloses a method for the determination of the structural strength of tires, in which the tire is illuminated with coherent light, the radiation diffusely reflected back from the tire is divided up in a twin beam interferometer into two beam parts, in the twin beam interferometer one of the two beam parts is tilted in relation to the other beam part as a shearing operation, in the twin beam interferometer one of the two beam parts is phase shifted in steps, the radiation diffusely reflected by the object being tested and split up into two beam parts and then united again is returned through components presenting an image of the surface of the tire with a large aperture to an electronic image sensor system and the signals produced by the image sensor system are digitalized and further processed to give a modulo 2xcfx80 image and the modulo 2xcfx80 image is confirmed as an output gray value image.
In accordance with the German patent publication 195 02 073 A1 the above mentioned method is further developed to the extent that the output gray value image is partially differentiated, a second gray value image identical to the output gray value image is produced and it is geometrically displaced in the shearing direction in relation to the output gray value image and is altered by a gray value which is constant over the entire image area and the second gray value image manipulated in this manner is subtracted from the output gray value image and so that a resulting gray value image is produced, from which any defects in the tire may be seen.
When it is considered that structural damage in tires and more particularly in the carcass including the belt, may in the case of car tires substantially impair the safety of the vehicle, it will be seen to be desirable for a device to be available able to perform tire testing.
The EP 0 884 574 discloses a method of testing tires wherein before and after an alteration in the tire pressure a respective interferogram is produced of the tire surface using coherent radiation and, from the interferogram, the information concerning any defects present in the tire is obtained. For testing a tire, the wheel having the tire to be tested is mounted on a balancing machine. A testing head located at the balancing machine, is moved towards the tire up to a preselected testing distance for deriving the interferogram. The testing on defects is carried out at a first testing segment of the tire. Thereafter, the wheel is rotated on by the balancing machine in the amount of a testing segment, and the last mentioned steps are repeated until the complete tire is tested. The tire testing apparatus comprises a balancing machine on which the wheel having the tire to be tested, is mounted, a positioning device for the testing head by means of which device the testing head is moved towards the tire up to a preselecting testing distance for deriving the interferograms, and a control device for the balancing machine in order to rotate the wheel by the amount of a testing segment forwards when the testing of the previous testing segment has been completed.
Since the costs for the test head are substantially dependent on the area which may be covered in a single measuring step, the above mentioned method is advantageous in that the costs for the test head may be reduced substantially in that a segmentwise testing of the tire is provided for, wherein a plurality of testing segments of the tire are subsequently brought into the field of view of the test head. On the other hand, the required investments are higher than necessary when the user only needs a tire testing device but no balancing machine.
It is the object of the invention is to create a tire testing method and apparatus rendering possible the testing of tires by as simple means as possible.
For this purpose, the method in accordance with the invention provides that, for testing a tire, the wheel which has the tire to be tested, is mounted on a rotatable shaft of a tire testing machine, that the distance of the tire from the test head is adjusted thereby that the wheel is shifted together with the shaft in the direction of the shaft, and that the shaft is locked thereafter, that the relative location of the test head with respect to the tire is adjusted thereby that the test head is, in order to bring it into position for differently sized tires, moved in a vertical direction, that the wheel is, thereafter, rotated further on by the amount of a testing segment by hand and locked mechanically when the next segment is in a test position in front of the test head, that the testing as to defects is carried on a first testing segment of the tire, and that the two last mentioned steps are repeated until the complete tire has been tested.
Some expenditure for hardware may be saved in that the wheel is rotated by hand. However, it has to be taken care that the wheel is rotated exactly by one segment since otherwise the position of the detected defects cannot be evaluated with a sufficient accuracy, and that the test head is positioned accurately in relation to the tire. This, however, is ensured by the way in which the machine is adjusted and by the mechanical locking of the shaft with the wheel. The test head may be arranged in a simple manner and without further means at an accurate testing position by such a simple scheme of movements.
In accordance with an advantageous development of the method, the relative position of the test head with respect to the tire adjusted thereby that the test head is moved in a vertical direction and perpendicular to the longitudinal direction of the shaft. Thereby, advantages are obtained with respect to the integration of the test head into the tire testing apparatus, and the adjustment of the test head can be carried out from above, which means from the console of the apparatus.
In accordance with an advantageous development of the method, the field of view of the test head is inspected by means of a camera which is arranged in the test head and is directed to the tire whereby the picture taken by the camera, is shown on a monitor. Thereby, it can be verified without further means when the test head is in the correct position with respect to the tire, and there are no further measurements necessary in order to verify this. It is also advantageous that the monitor which is already provided for, is also used for this purpose.
In accordance with a further advantageous embodiment of the method of the invention, the values necessary for the further rotation of the wheel, for example the tire size, are input into a computer, and the computer issues an information about the number of segments which are required in order to test the complete tire. If the sizes are stored in form of a table, this table can concurrently be updated by inputs made by hand such that the effort for the adjustment for a test run is becoming ever smaller.
A further advantageous embodiment of the method of the invention is characterized in that the number of the required segments is adjusted at the shaft. This adjustment is done by hand while using the information given from the computer. Therefore, the corresponding adjustment can be made with a minimum of hardware.
A further advantageous embodiment of the method of the invention is characterized in that, upon adjustment of the distance between the test head and the tire, this distance is watched and an indication is given when the test head has reached the desired distance, and that the test head is, thereafter, locked. Thereby, a secure, fast and accurate adjustment of the test head with respect to the tire is possible.
A further advantageous embodiment of the method of the invention is characterized in that the pressure of the tire is reduced for each test step, whereby, after completing the tests, the pressure is brought back to the nominal pressure. With this method, the changing of the pressure of the tire may be carried out during the whole test cycle in which the test segments are measured successively at a minimum of time loss, since the changing of the pressure from the first test step to the second test step begins at the final pressure which is present at the end of the first test step. Furthermore, the tire has to be at rest for a given time period after each change of pressure such that the test results are not influenced by the continued movements which are caused by the pressure change. Therefore, the time needed for such a recovery or rest time period is minimized when the number of pressure changes which are made during a test cycle, is brought to a minimum. The number of recovery or rest time periods would increase when the tire pressure would be brought to nominal pressure after each tire test step with respect to a specific portion of the tire.
For solving the above object, the tire testing apparatus according to the invention comprising a air pressure device for changing the tire pressure as well as a test head and a computer which before and after an alteration in the tire pressure produce a respective interferogram of the tire surface using coherent radiation and, from the interferogram, obtain the information concerning any defects present in the tire is characterized by a rotatably supported shaft on which the wheel with the tire to be tested is mounted, by a bearing device by which the wheel with the shaft is shiftable in longitudinal direction of the shaft, by a shaft locking device by which the shaft is locked with respect to a movement in the longitudinal direction of the shaft thereafter, by a guiding device by which the test head is moved in a radial direction of the wheel, by a wheel locking device by which the wheel is mechanically locked when the wheel is further rotated by hand by an amount of a test segment and when the next segment is in test position in front of the test head, and by a starting device by which the testing on defects of a first test segments of the tire is started.
An advantageous embodiment of the tire testing apparatus according to the invention is characterized in that the computer comprises a storage in which a table is stored which contains data as to the number of segments which are required for rotating on the wheel in dependence of the size of the wheel. The storage in the computer ensures that as little as possible knowledge is necessary for operating the apparatus.
An advantageous embodiment of the tire testing apparatus according to the invention is characterized in that the bearing device comprises a rotatably supported outer shaft and an inner shaft rotatably supported within the outer shaft as well as an unlockable locking device connecting the outer shaft to the inner shaft, whereby in particular the locking device comprises a clamping hub between the outer shaft and the inner shaft and a lockable locking wheel, whereby the locking of the locking device may be loosened or tightened by rotating the inner shaft. Thereby, the shaft with the wheel may be shifted in longitudinal direction of the shaft in a simple mechanical way in order to implement the desired distance between the test head and the tire.
An advantageous embodiment of the tire testing apparatus according to the invention is characterized in that the guiding device for the test head comprises a crank drive which is mechanically or hydraulically or electromagnetically lockable whereby the crank drive is arranged in a vertical direction and perpendicular to the longitudinal direction of the shaft. Thereby, a simple and accurate positioning of the test head is possible without a specific knowledge or ability being required at the side of the person operating the machine.
In this context it is, furthermore, advantageous if the guiding device and the test head are integrated into a housing on the tire testing apparatus. This embodiment of the invention has the advantage that the volume required by the machine, is minimized, and that the test head is protected somehow within the housing of the tire testing apparatus which is a profound advantage having in mind the rough environment being present at automobile service shops where such machines are used.
An advantageous embodiment of the tire testing apparatus according to the invention is characterized by a camera which is arranged in the test head and which is directed to the tire, whereby the field of view of the test head is inspected by means of the camera by displaying the picture taken from the camera on the monitor.
An advantageous embodiment of the tire testing apparatus according to the invention is characterized in that the wheel locking device comprises index discs arranged on the outer shaft having index recesses the number of which corresponds to a different number of test segments, and that a lever with a cam is provided which engages the index recesses with the cam.
An advantageous embodiment of the tire testing apparatus according to the invention is characterized by a distance setting device for setting the distance between the test head and the tire.
An advantageous embodiment of the tire testing apparatus according to the invention is characterized in that the distance adjusting device comprises a mechanical keying device on the test head which keying device touches the tire upon reaching the test distance. This is a mechanical version of the distance adjusting device which is adapted to the rough environment in a simple way.
An advantageous embodiment of the tire testing apparatus according to the invention is characterized by a valve which may be adjusted with respect to the size of its opening as well as with respect to the opening time duration. Such a valve enables a fast and automatic adjustment of the pressure of the tire under the control of a computer which only controls the size of the valve opening and the opening time duration of the valve. This is also an advantage with respect to minimizing the required time duration for carrying out a complete test cycle.
An advantageous embodiment of the tire testing apparatus according to the invention is characterized by a main or central control device for controlling the air pressure in the tire whereby the pressure in the tire is to be reduced for each test step by one step and has to be brought back to the nominal pressure upon termination of a test. As already mentioned, this minimizes the required time for carrying out a complete test method cycle.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.
Working embodiments of the invention will now be described with reference to the accompanying drawings.